Production of aromatics by thermal cracking



July. 6, 1948- R. MQ sHEPARDsoN ErAl. 2,444,855

PRODUCTION OF AROMATICS BY THERMAL CRACKING v Filed Dec. 27, 1940FRAcr/aNA Tuve 01.0 HIV Z-Il "dmz Fg n 42 450 @www REFRICERAT//Vc Y 36 yS/TRIPP/L Illl WASH A TOWER /IVAE T Patented July 6,1948

PRODUCTION F AROMATICS BY THERMAL CRACKING Robert M. Shepardson,Cranford, and litoyv L. Mathiasen, Fords, N. J., assignors to StandardOil Development Company, a corporation of Delaware Application December27, 1940, Serial No. 371,870

4 Claims. (Cl. 260673.5)

The present invention relates to improvements in the production ofaromatics, including toluene, from non-benzenoid hydrocarbons, and moreparticularly it relates to processes for producing nitration gradetoluene, entirely satisfactory for the manufacture of tri-nitro toluene,by cracking a paraffnic or naphthenic gas oil under certain specifiedconditions, fractionating the cracked products, recovering a fractionboiling within the range of from 200250 F. and subjecting the latterfraction to solvent extraction to recover the desired aromatic. Bypracticing our invention according to the present disclosure, we havebeen able to secure toluene having a purity greater than 99 per cent,or, in other words, we have secured toluene of nitratable grade.

One object of our' invention, therefore, is to crack a gas oilthermally, preferably a gas oil having an end boiling point not aboveapproximately 850 F. and containing a preponderance of parafiinic and/ornaphthenic constituents.

Another object of our invention is to thermally crack gas oil in arelatively short period of time at a high temperature, thereafter tofractionate the cracked products and to recover a fraction boilingwithin the range of from about 200250 F. and thereafter selectivelydissolving from this fraction very pure toluene which may be separated.from the solvent in known manner.

Another object of our invention is to produce aromatic hydrocarbons fromnon-benzenoid hydrocarbons.

Other and further objects of our invention will appear from the ensuingdescription and claims, reference being had to the accompanying draw-The drawing represents schematically a system or combination ofapparatus elements in which our invention may be carried into eifect.

Referring in detail to the drawing, a gas oil having an A. P. I. gravityof about 33 and boiling within the range of from about 500 to 750 F. wasintroduced into the system through line I and pump 2 into line 6 inwhich this material was combined with approximately 80 mol per cent cfsteaznbased on the mixture of steam and hydrocarbons introduced throughline 4, thence discharged into a coil 3 disposed in a furnace setting 5where the feed stock was heated to a temperature of about 1200 F. whilemaintaining a pressure of about 8 lbs./sq. in. gauge, and in which thefeed rate to the coil was about 0.5 volume of cold oil per volume ofcoil per hour. The oil was permitted to remain in the coil for a periodof 2.7 seconds. Under the conditions specied, it later turned out, aswill more fully appear hereinafter, that this operation resulted in theproduction of 45 per cent aromatics in the gasoline. The crackedproducts were withdrawn from coil 3 through line l0 and thencedischarged into a fractionating column |2. A heavy fraction suitable foruse as a fuel oil w-as withdrawn from fractionatng column |2 throughline 30 and a gas oil fraction through line 3|. This gas oil may berecycled to line 6 by pump 1 and line 8, but we have found this materialto be a less satisfactory charge stock than virgin materials and preferto dispose of this fraction elsewhere. The gasoline and gaseousfractions were withdrawn from the top of column I2 through line 32,thence through condenser I4 and to separating drum I5 by means of line33. Water was separated in drum I5 and withdrawn through line IB. Gaswas removed from separating drum I5 through line I1 and gasoline throughline I8, each being compressed or pumped to about lbs./sq. in. gauge bymeans of compressor I9 and pump 20, after which these fractions werecombined in line 23 and discharged into separating drum 2|. Thiscompression was necessary to recover the small quantities of aromaticscontained in the gas fraction separated in drum l5 at' atmosphericpressure. Gas was withdrawn from separating drum 2| through line 22 andthe distillate through line 24 into coil 35 disposed in furnace setting3'1, following which the vapors were fractionated in column 26. Materialboiling above approximately 250 F. and free of toluene was withdrawnthrough line 25 and the overhead fraction containing toluene wastransferred through line 21 into fractionating column 28. Materialsboiling below approximately 200 F. and free of toluene were withdrawnthrough line 29 and the crude toluenecontaining fraction through line34. The gaseous fractions leaving the system through lines 22 and 29were found to be rich in olefin fractions such as ethylene, propylene,and butylene, as well as butadiene and higher conjugated diolens. Thesematerials are particularly valuable for the manufacture of high octaneblending agents by polymerization or alkylation, or for lay-productmanufacture. The toluene-containing fraction withdrawn fromfractionating tower 20 through line 34 was cooled with water in cooler36 thence discharged through line 38 into a refrigeration zone 40 whereit was cooled to a temperature in the neighborhood say of 40 F. Therefrigeration may be effected by liquid prop-ane or any other known orconvenient method. The refrigerated fraction was then withdrawn fromzone 40 through line 42 and discharged into a solvent treating tower 46at a point near the bottom thereof, as indicated. At the same time,chilled liquid SO2 was discharged into solvent treating tower 46 throughline 59 at a point near the top thereof. In the tower the hydrocarbonoil passes upwardly against the downwardly flowing SO2, thus forming aramnate and an extract fraction. The rafinate portion, which is enrichedin paraiiinic constituents and also containing some SO2, was withdrawnfrom tower 46 through line 52 into stripper 53 in which the SO2 isremoved through line 55 and the SO2-free raffinate through line 54. TheSO2 from the rafnate thence passes through line 55 to SO2 storage drum80 from which point it was recycled through line 56 and pump 51 by meansof line 58 to the extraction tower 46.

'I'he extract fraction, on the other hand, was withdrawn through line 65and then discharged into a washing tower. 61 at a point near the topthereof. At the same time, isopentane was discharged into tower 61through line 68 near the bottom thereof. The effect of the iso-pentaneis to displace the non-aromatic hydrocarbons contained in the SO2extract and substitute isopentane so that the extract at the bottom ofthe tower will contain SO2. aromatic hydrocarbons, and substantially nonon-aromatic hydrocarbons except isopentane. This result is accomplishedby a sort of mass action effect wherein the large preponderance ofisopentane over the non-benzenoid hydrocarbons in the extract causessubstantially the complete removal of the latter from the extract. Theadvantage of replacing the hydrocarbons originally in the extract withisopentane is that the aromatics and isopentane may eventually beseparated from each other by simple distillation due to the fact thatthere is a rather wide hiatus in the boiling points between the twosubstances. yThe non-benzenoid hydrocarbons originally in the SO2extract had a boiling point in close proximity to that of the aromaticsand therefore a separation could not be effected by simple distillation.The non-benzenoid hydrocarbons originally in the extract, together withthe isopentane, are withdrawn from the top of tower 61 through line 10,from which they may be delivered through coil 1| disposed in furnacesetting 63 and thence through line 12 into tower |2| in which isopentaneis separated from the higher boiling non-benzenoid hydrocarbons, theisopentane being returned through line |25 to cooler 13 thence tostorage drum 18 through line 14. Isopentane for tower 61 is suppliedfrom storage drum 16 through line 11 and pump 8i' thence to line 68. TheSO: extract is withdrawn from the bottom of the tower through line 15,delivered to stripper 18 in which the SO2 may be separated from thearomatics, compressed, refrigerated and return through line 19 tostorage drum ,80 and returned through line 56, pump 51 and thence line5l) to tower 46. The aromatic compounds are withdrawn from the solventrecovery system through line 82 and thence intimately mixed with anacid. such as sulfuric acid, introduced through line 92 at point 93,this mixture being discharged into separating drum 90 through line 9|.Acid sludge is withdrawn from separating drum 9D through line 94 and theacid treated oil through line 96 into tower 98. A dilute solution ofsome alkali such as sodium hydroxide in water was discharged into tower98 through line |80 and passes downward- '4 ly against the upwardlyflowing aromatics. thus neutralizing and washing any acid associatedwith the said aromatics. The washing medium was withdrawn from tower 98through line |92. This acid treating step was necessary to .remove thevery small quantity of oleflns present in the aromatic extract, theseolens being objectionable in nitration grade toluene. The purifiedaromatics and isopentane mixture was withdrawn from wash tower 98through line |88 and deliveredto a heating coil 84 where thehydrocarbons are heated to vaporization temperature, thence dischargedthrough line ||2 into a fractionating column H4. Mixed xyienes and asmall quantity of toluene are withdrawn from the bottom of fractionatingcolumn III through line i I3, the major portion of the toluene passingoverhead as vapor through line H5 into the fractionating tower |I1.Puried toluene of better than 99 per cent purity was withdrawn fromtower H1 a through line I i6 thence discharged into a cooler H8 andnally through line |28 into a receiving drum |28. Overhead vapors fromfractionating column H1 consisting of isopentane, benzene, and a smallquantity of toluene pass overhead through line I9 in which they arecombined with the isopentane fraction from extraction tower 61. 'I'hecombined stream is fractionated in column |2| into isopentane as anoverhead fraction for return to the extraction system and a bottomsfraction consisting of small quantities of benzene, toluene andnon-benzenoid hydrocarbons. This bottoms fraction is withdrawn fromfractionating column |2| through line |22 and combined with the mixedxylene fraction from tower H4, the mixture being transferred throughline |23, pump |24 and line |28 to the fractionating system followingthe cracking operation for recovery of the small quantities of toluenewhich escaped the extraction or distillation zones in the rst-passthrough the equipment.

YIn the preceding description, all of the equipment necessary to eilectthe separation of isopentane and/or SO2 from the products has not beenillustrated because these means are well known to those skilled in thesolvent extraction art. Likewise, the method of refrigerating the SO2and the hydrocarbons has not been described in detail because variousmethods are known in the art for accomplishing these results.

In the preceding example, we have set forth a preferred modification ofour invention, but it is to be distinctly understood that our inventionis not limited to these precise details. For example in the crackingcoil 9, we may use the following range of conditions:

Pressure Subatmospheric to lbs` Temperature 1100 F.-1400 F. Time ofresidence in coil, in`seconds 0.515.0

Although steam is not absolutely necessary in the above describedcracking operation, we have found that the use of steam` or any othergaseous medium is desirable as it permits the production of a greaterquantity of aromatics under otherwise constant operating conditions.Also, the use of steam appears preferable to gaseous fractions in thatit can easily be condensed and removed from the system.

Furthermore, with respect to the washing medium or diluent employed intower 61, the same need not be isopentane but may be any non-aromatichydrocarbon which has a diierent boiling point from the aromaticscontained in said extract. Instead of using SO2, we may use any solventwhich has a greater solvent action for aromatic hydrocarbons than fornon-aromatic hydrocarbons. As to the charging stock, it is pointed outthat for best results the same should be substantially free of olens.

Furthermore, this invention is not limited to the yproduction ofsubstantially pure toluene, as benzene of equal purity can be producedby charging a fraction boiling from approximately 150 F. to 200 F. tothe extraction step. Also, mixed xylenes containing ortho, meta, andpara-xylene and ethyl benzene can be produced in high purity by charginga fraction boiling from approximately 260 F. to 310 F. to the extractionstep.

To recapitulate, our invention comprises cracking a petroleum oilthermally at high temperatures and during a short residence time in thecracking coil, fractionating and recovering a cut boiling within therange of the desired aromatic, subjecting this latter fraction tosolvent extraction with a material such as S02 having a preferentialsolvent action for aromatics, removing the SO: extract to a washingtower where it is` contracted with a non-benzenoid hydrocarbon having adifferent boiling point than the desired aromatic so as to form a secondextract consisting essentially of SO2, or the like, the desired aromaticandthe washing agent separating the SO2 or other aromatic solvent fromthe hydrocarbons, and iinally distilling the hydrocarbons to recover thedesired aromatic.

What we claim is:

i. A method of producing nitration grade toluene o! over 99% purity fromparamnic petroleum gas oil hydrocarbons which comprises heating parainicpetroleum gas oil hydrocarbons of about 500 to 700 F. boiling range inthe presence of a large amount of steam to a temperature of about 1200to 1400 F. for a period of about 1/2 to 15 seconds at a pressure of notmore than 150 lbs/sq. in., fractionating the reaction products,recovering a fraction boiling within the range of from about 200 F. to250 F., condensing said fraction, cooling said condensed fraction in arefrigeration zone, treating said cooled fraction with liquid sulfurdioxide to form an extract, washing said extract with isopentane,separating sulfur dioxide from said extract, treating said extract withacid to remove oleiins, neutralizing the acid-treated extract andfractionating the extract to recover nitration grade toluene.

2. A method of producing nitration grade toluene o1' over 99% purityfrom paramnic petroleum gas oil hydrocarbons boiling within the ingwithin the range oi from about 200 to 250 F., condensing said fraction,cooling said condensed fraction to a temperature or about 40 F.,treating said cooled fraction with liquid sulfur dioxide to form anextract, washing said extract with isopentane, separating sulfur dioxidefrom said extract, treating said extract with acid to remove olefins,neutralizing the acid-treated extract and fractionating the extract torecover nitration grade toluene. 3. In the process of recovering toluenefrom a hydrocarbon fraction boiling between about 200 and about 250 F.obtained by thermally steam-cracking paramnic gas oil hydrocarbonsboiling within the range from about 500 to 700 F. at temperatures ofabout 1200 to 1400 F., contact times of about 1/2 to 15 seconds andpressures not higher than 150 lbs/sq. in., the steps comprisingcondensing said fraction, cooling said condensed fraction in arefrigeration zone, treating said cooled fraction with liquid sulfurdioxide to form an extract, washing said extract with isopentane,separating sulfur dioxide from said extract, treating said extract withacid to remove olefins, neutralizing the acid-treated extract andfractionating the extract to recover nitration grade toluene. i

4. The method set forth in claim 3 wherein said condensed fraction iscooled to a temperature of range of from about 500 to about 700 F. whichcomprises heating the hydrocarbons in the presence of about mol o! steamto a temperature of about 1200 F. for a'period of about 2.7 seconds at apressure of about 8 lbs/sq. in.. fractionating the reaction products,recovering a fraction boilabout 40 F.

ROBERT M. SHEPARDSON. ROY L. MATHIASEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,871,694 Ihrig Aug. 16, 19321,912,349 Tuttle May 30, 1933 2,133,344 Cooke Oct. 18, 1938 2,139,000Cohen Dec. 6, 1938 2,143,472 Boultbee Jan. 10, 1939 2,218,495 BalcarOct. 15, 1940 12,263,557 Greenwalt Nov. 25, 1941 2,288,126 Dunn et als--- June 3 0, 1942 FOREIGN PATENTS Number Country Date 441,104 GreatBritain Jan. 13, 1936 443,545 Great Britain 1936 459,189 Great BritainJan. 4, 1937 459,595 Great Britain Jan. 11, 1937 482,431 Great BritainMar. 29, 1938 491,992 Great Britain Sept. 13, 1938 OTHER REFERENCESGroll: Vapor-Phase Cracking, Ind. and Eng. Chem., vol. 25, No. 7, pages784-797 (14 pages) (pages 789- are especially pertinent) (July 1933).

